A. Field of the Invention
This invention relates to a radio transceiver antenna which is tunable to a range of radio frequencies. Radio transceivers are quite sensitive to antenna performance, requiring that the antenna have a sufficiently low Voltage Standing Wave Ratio (VSWR) and sufficiently high power handling capacity to efficiently radiate transmitter power output under varying environmental conditions. Such antennas are employed universally by Maritime, Aviation, Military and Government services, and by the general public as well, and it is the use of mobile transceivers and antennas which is the focal point of this invention.
It is the High Frequency (HF) range of radio transmission with which this invention is particularly concerned, although it is to be understood that the tuning concepts herein disclosed are equally applicable to other radio frequency bands as may be required. With respect to the HF range covering 1.6 to 30 MHz frequencies, the size, and particularly the length of the antenna is frequently a limiting factor on mobile transceiver performance. Assuming that a transceiver is installed on and transported by a moving vehicle, clearance along most highways and roadways is 14 feet, whereas the optimum vertical height of a properly tuned antenna can far exceed said highway or roadway clearance. Therefore, it is an object of this invention to increase and decrease the tuned, electrical antenna length (as distinguished from physical height), thereby avoiding limitations imposed by highway and/or roadway vertical clearance.
B. Description of Background Art
Heretofore, some RF antennas have been tuned by means of inserting coils into an antenna circuit that extend the antenna""s effective length without extending the height thereof. In practice, individual coils have been employed and installed for each radio frequency to be matched. Or, complicated and expensive Antenna Tuners have been used, but they are bulky extra equipment.
It is therefore a general object of this invention to provide an antenna which can be fine tuned to any radio frequency within a specified range, and in particular for example in this disclosure, the practical High Frequency HF range from 3.5 to 30 MHz In practice, the antenna is center loaded with a coil and a longitudinally movable commutator that adjustably extends the effective length of the antenna.
It is another object of the present invention to provide an antenna which includes an actuator mechanism that is energizable by a remote switch, by which means the antenna can be adjustably tuned from a transceiver located at some distance from the antenna.
Another object of the invention is to provide matching impedance of the antenna by means of a shunt to ground, as will be described.
Another object of the invention is to provide a frequency adjustable mobile antenna which includes a first disk-shaped commutator having a circumferential surface for longitudinally movable commutation with convolutions of an upper portion of a coil, the electrical length of which upper coil portion determines the resonant frequency of the antenna.
Another object of the invention is to provide a frequency adjustable antenna having in addition to a first disk-shaped commutator for longitudinally movable tunable commutation with the upper portion of a coil, a second, lower disk-shaped contactor for resiliently and electrically conductively contacting a coaxially located shaft longitudinally slidable within the lower contactor, the contactor being in electrical contact with the lower end of the coil winding and the upper end of the shaft being in electrical contact with the disk-shaped commutator, whereby the lower portion of the coil is electrically shorted or xe2x80x9cRF de-coupled,xe2x80x9d thereby suppressing any harmonic currents which might otherwise be generated in the lower portion of the coil by auto transformer action.
Another object of the invention is to provide a method of making a coil assembly for a frequency adjustable antenna which includes the steps of winding a coil on a helically grooved mandrel, inserting the coil and mandrel into coil housing having formed in an inner cylindrical wall surface thereof a helical groove, expanding the diameter of the coil to thereby release it from the mandrel grooves and loosely seat the coil convolutions into the convolutions of the helical groove within the coil housing, removing the coil housing from the mandrel, and further expanding the diameter of the coil to rigidly fix the coil within the coil housing groove.
Various other objects and advantages of the present invention, and its most novel features, will become apparent to those skilled in the art by perusing the accompanying specification, drawings and claims.
It is to be understood that although the invention disclosed herein is fully capable of achieving the objects and providing the advantages described, the characteristics of the invention described herein are merely illustrative of the preferred embodiments. Accordingly, I do not intend that the scope of my exclusive rights and privileges in the invention be limited to details of the embodiments described. I do intend that equivalents, adaptations and modifications of the invention reasonably inferable from the description contained herein be included within the scope of the invention as defined by the appended claims.
Briefly stated the present invention includes a frequency adjustable antenna for use with radio transceivers, particularly those used in vehicles. One embodiment of the invention includes a lower, electrically conductive hollow tubular mast section electrically isolated from a mounting bracket and having a radio frequency connection to a transceiver, and an upper electrically conductive extensible mast section insulated electrically from the lower mast section and adapted to hold an elongated whip antenna. The upper and lower mast sections are fastened in coaxial alignment therewith to the upper and lower ends of a hollow cylindrical coil housing, which is made of an electrically nonconductive material and has formed in the inner cylindrical wall surface thereof an elongated helical groove. The groove holds conformally therewithin convolutions of an electrically conductive tuning coil, the lower end of which is in electrical contact with the lower mast section. A disk-shaped contactor means or commutator fits coaxially within the coil, the commutator having a circumferential spring member which has a resilient outer circumferential surface which is in electrically conductive, longitudinally slidable contact with inner circumferential surfaces of convolutions of the tuning coil, the contactor being carried by and in electrical contact with the upper mast section. An electric motor and lead screw mechanism within a hollow interior space of the lower mast section of the antenna raises and lowers the upper extensible mast section and the commutator in response to external command signals, thus interposing more or less coil convolutions in series between the lower end of the upper mast and the lower mast, thus resonating the antenna to lower or higher frequencies, respectively.
In another embodiment of an antenna according to the present invention, the conductive whip at the upper end of the antenna is fixed in a cap attached to the upper end of an insulated coil housing and is electrically connected to the upper end of a tuning coil within the housing, and remains stationary. In this embodiment, a commutator disk at the upper end of a conductive shaft is raised or lowered to interpose less or more turns between the lower end of the shaft and the whip to tune the antenna. This embodiment also includes an RF de-coupler which has an annular ring-shaped spring member that has a resilient inner circumferential surface in longitudinally slidable contact with the outer surface of the conductive shaft, and an outer surface in electrically conductive contact with the lower end lead of the coil and a lower conductive mast, thus shorting out the lower portion of the coil and thereby suppressing harmonics or subharmonic currents from being induced therein.
According to a method of making a coil assembly of the type described above for the frequency adjustable mobile antenna, wire is wound into a helical groove formed in a mandrel of smaller diameter than the inner diameter of an elongated cylindrical coil housing having formed in an inner cylindrical wall surface thereof a helical housing groove, by rotating the mandrel in a first direction, a coil housing is slipped over the wound coil on the mandrel, the mandrel is turned in an opposite direction to cause coil convolutions in the mandrel groove to increase in diameter and thereby spring out of the helical mandrel groove and into the helical coil housing groove, and wire from a supply reel is severed, whereupon the coil and housing are removed from the mandrel, and a resilient paddle forcibly inserted sequentially into opposite longitudinal ends of the coil bore and turned to further increase the diameter of the coil helix and thereby securely seat the coil within the coil housing.